The high resistance of PVC against combustion as well as its low price and favourable processing properties are among the main reasons why this polymer is still one of the most widely used plastics where an optimum balance of price, processing ease, high strength and resistance to microbial degradation is required, such as in weather-exposed construction elements including tubings, panels and the like products.
According to the state of the art PVC must be compounded with stabilizers before it can be used for the manufacture of finished or semifinished articles, such as by moulding methods that involve extrusion. As used herein, the term "compounding" refers to a separate processing step in which molten or thermally plasticized PVC (i.e. in a heated state) is mixed with at least one constituent containing a stabilizing additive so as to form an essentially uniform material which is solidified to form a product that can be sold to the processing industry, e.g. in the form of pellets or granules.
Obviously, compounding of PVC involves a considerable energy consumption and is a significant cost factor. However, previous attempts to avoid compounding have failed and it has been generally assumed that compounding is a sine-qua-non requirement of PVC production because otherwise the PVC constituent would undergo substantial decomposition upon extrusion.